Glass yarn, produced from glass fibers, is woven into cloth and used as filler in various types of circuit board polymeric laminates. The insulation resistance (IR) of these laminates is measured before and after soaking in distilled water at 50.degree. C. for 48 hours. IR degradation has been found to vary from glass batch to glass batch and presents a serious problem in circuit board manufacture.
The method of this invention is directed towards the solution of that problem, as well as towards increasing the IR of glass fibers.